Dryer section pocket ventilation



g- 29, 1-967 G. KRIKORIAN ETAL 3,337,958

DRYER SECTION POCKET VENTILATION Filed Jan. 27, 1966 United StatesPatent 3,337,968 DRYER SECTION POCKET VENTILATION Garo Krikorian,Paxton, and Nicolas Martin Reitzel, Boylston, Mass., assignors to RiceBarton Corporation, Worcester, Mass., a corporation of MassachusettsFiled Jan. 27, 1966, Ser. No. 523,355 4 Claims. (Cl. 34111) Thisinvention relates to the dryer section of a paper machine and isparticularly concerned with new and improved arrangements forventilating uniformly the pockets which are defined by a felt rollwrapped by a felt and one or more dryer drums, the runs of felt betweenrolls and drums and the runs of sheet between drums.

In the conventional dryer section with top and bottom rows of dryerdrums, two felts, and the paper web running between drums of the tworows alternately, two series of so-called pockets are formed which areopen only at each side of the machine. A pocket of one series is formedbetween an upper felt roll wrapped by the felt and the adjacent lowerdryer drum, the remaining walls of the pocket comprising runs of thetravelling upper felt and runs of the web itself which separates fromthe upper felt at the next succeeding upper dryer drum. The pocketsof-the other (lower) series are similarly defined by the wrapped lowerfelt rolls and opposing upper dryer drums, runs of the lower felt andruns of the paper web.

Because of the presence of the pockets, humidity at the center of themachine is higher than at the edges where evaporated moisture can escapemore readily, resulting in a reduced drying rate at the center andconcomitant non-uniform moisture content of the dried web. If moisturecontent is plotted against the width of the sheet the resulting graphwill be low at each end and high in the middle, sometimes referred to asthe moisture profile of the web.

It has been proposed to ventilate the above mentioned pockets by blowingheated dry air through the felt from the outside into the pockets fromplenum chambers'located closely adjacent to runs of the felt betweendryer drums and a felt roll. For example, in US. Patent 3,1l0,- 575,there is disclosed such an arrangement including provision forsimultaneously withdrawing air from the pocket through another adjacentrun of the felt by suction means arranged outside such run of the felt.

An inherent difficulty with the arrangements previously proposed is toprovide adequate sealing between the edges of the air delivery duct andthe felt to force significant quantities of air through the felt. Infact, it is well nigh impossible to produce an adequate air flow byknown means through any but the most permeable felts.

The object of the invention is to provide an improved apparatus forventilating the pockets formed in a paper machine dryer by supplying airto the pockets from the outside through a run of the felt which willdevelop suflicient static pressure to pass effective quantities of airthrough felts including even felts having poor permeability and whereinlosses through the seals are minimized.

In accordance with the invention there is provided in a dryer section ofa paper machine apparatus for moisture profile control by ventilatingpockets defined by the wrapped felt rolls, the dryer drums, runs of feltand the paper Web, comprising a plurality of plenums arranged on theside of the felt which does not contact the Web and opening against thefelt, each plenum being positioned adjacent a run of the felt where thelatter is separated from the paper web and arranged to force dry airthrough the felt into the pockets. The edges of the open ing which facesthe felt are sealed by flexible inwardly directed seals bearing againstthe felt at either side and by similar seals at each end one of whichdirectly engages the surface of the felt roll and the other of which3,337,968 Patented Aug. 29, 1967 ice extends transversely inwardlyacross the running felt and bears thereagainst.

Further objects, features and advantages of the invention will appearfrom the following detailed description of a presently preferredembodiment thereof taken in conjunction with the accompanying drawingsin which:

FIG. 1 is a partially diagrammatic view on a reduced scale of a portionof the dryer section of a paper machine embodying the invention; a

FIG. 2 is a cross-sectional view on an enlarged scale of one of the airsupply units of the invention located outside a pocket adjacent a run offelt;

FIG. 3 is a section on line 3-3 of FIG; 2; and

FIG. 4 is a detail view in side elevation of a portion of the plenumunit shown in FIG. 2 illustrating particularly the operation of the sidesealing members during passage of a clipped felt joint under the plenum.

Referring to the drawings, banks of upper dryer drums 10 are arranged instaggered relation to banks of lower dryer drums 12. Beneath each upperdrum 10 is mounted a felt roll 14 and above each lower dryer drum 12 ismounted a felt roll 16. The upper felt 18 passes alternately from drum10 to roll 16 and then to the next drum 10 wrapping the same in part andpressing the paper web 20 against the surfaces of the dryer rolls.

It will be seen that two series of pockets are formed in the dryersection, each being defined by one felt roll and one dryer drum and theruns of felt and paper web. Moisture driven from the web by the dryerdrum will find it more difiicult to escape from the middle portions ofthe pockets than from the side portions thus producing the undesiredmoisture profile in the sheet.

To ventilate the pockets and make more uniform the moisture profilethere is mounted adjacent the run of felt as it leaves each dryer drumand before it wraps the next felt roll an end fed manifold orsub-divided plenum chamber 22 extending the width of the felt andlocated on the side of the felt which does not contact the paper web.The plenum 22 is subdivided into several passageways, in this instancethree designated by the numerals 22a, 22b, and 220. The passagesterminate against a perforated plate 24 and, preferably the centralpassage 22b opens against the central one-half of the plate 24 and theother passages occupy each the remaining one quarter of the areathereof.

On the side of the plate 24 toward the felt 18 an air discharge chamberis formed to force air from the plenum through the web into the adjacentpocket. This chamber is defined by the plate 24, the felt 18 itself, andflexible side seals 26 and flexible end seal 28 and end seal 30. Baffles35 are-located in line with dividing walls 220 and 22b of plenum 22.Baflies 35 operate in close but noncontacting relation with felt 18 toproduce gradual pressure transitions between plenum zones. The end seal28 is a trailing flexible strip which bears against the felt surface toprovide a seal while the seal 30, on the contrary, bears directlyagainst the unwrapped surface of the roll 16 where its action .will bethe most effective. The side seals 26 are of the usual flexible contacttype and bear against the felt at locations slightly inwardly spacedfrom the marginal edges of the felt.

The presently preferred construction and arrangement of the sealingstrips by means of which adequate sealing is provided between the edgesof the air delivery duct and felt Will be described in detail asfollows:

A flexible end sealing strip 28 which closes the felt entering end ofthe plenum discharge chamber is formed of a flexible material of goodwear properties capable of withstanding the air temperatures utilized. Aglassfiber reinforced polyfluoroethylene material for example, has beenfound suitable for this purpose. The sealing strip 28 is mounted in arecess in the plenum wall 22 and retained by a clamp or clamps 46 heldby screws 48. The sealing strip 28 is wider than the separation of theplenum wall 22 from the felt 18 and is bent or sprung inwardly under theplenum 22 and in the direction of travel of the felt. Bending thesealing strip 28 inwardly produces sufiicient contact pressure againstthe felt to reduce leakage to a minimum. Due to the flexible nature ofthe seal 28, the seal adapts itself continuously to the rough surface ofthe travelling felt and to any substantial discontinuities in the 'feltsuch as a felt seam. Static air pressure within the plenum presses onthe inner surface of the sealing strip 28, further increasing theloading of the strip 28 against the felt 18. As plenum static airpressure is increased, the pressure on the inside of the sealing strip28 increases proportionally, increasing the sealing load on the felt 18and providing effective sealing at plenum pressures, which are in excessof pressures found practicable in the prior art. The side sealing strips26 are similarly formed of a'heat, and wear, resistant resilientmaterial, such as the glass-fiber reinforced polyfiuoroethylenematerial, above referred to, and are mounted in slots extending alongthe bottom edges of the plenum side walls so that they slopeinwardly'under the plenum 22 into engagement with the travelling felt.The strips 26 are held in sealing engagement with the felt by theresilience of the material, reinforced by the static pressure of the aircolumn in the manner above described for the sealing strip 28.

The action of a substantial discontinuity in the felt 18, whentravelling in contact with the sealing strips 26 isshown in FIG. 4. Aclipped felt seam consisting of clips 50 and pin 52 joining abuttingends of felt 18, and protected from contact with the paper by a flap 54will deflect the engaged portion of the strip 26 further inwardly whileother portions of the strip continue to be pressed inwardly so thatcontact with felt 18 is maintained undiminished. Each strip 26 isrelieved on leading edge at 56 (see FIG. 4) to prevent seam clips 50from damaging the strip 26 on initial contact. The sealing strip 30,.which closes the felt leaving edge of the plenum discharge chamber, actsagainst roll 16, and is made preferably of a rigid material. The sealingstrip 30 is mounted in a recess in the plenum wall 22, being retained asshown in FIG. 2 by a suitable clamp 58 and screws 60. Springs 62 loadthe rigid strip 30 against roll 16 with sufficient pressure to sealagainst loss of air in plenum 22. Alternatively, the seal 30 may be offlexible construction similar to seals 26 and seal 28. It is notedparticularly thatthe seal 30, by virtue of engaging the roll 16, issloped in the direction of the moving surface, thus minimizing thefriction and wear therebetween while at the same time advantage is takenof the air pressure built up within the discharge chamber to maintainthe seal.

The plenum 22 is fed by a duct 40 which extends to one or both sides ofthe machine and may be connected to a suitable source of heated, dry airunder pressure. Dampers 42 serve to control the flow of air to therespective passages 22a, 22b, and 22c, so that the volume of airsupplied at different locations along the width of each pocket may becontrolled to produce the desired moisture level in the paper web beingdried.

Of particular importance is the effectiveness of sealing the outgoingedge of the discharge chamber against the surface of a roll 16 ratherthan against the felt thereby to very substantially increase the staticpressure in the 4 discharge chamber such as to pass eifective volumes ofair through even relatively impermeable felts.

While there is herein disclosed and described a presently preferredembodiment of the invention it will nevertheless be understood that thesame is susceptible of modifications and changesby those skilled in theart and therefore it is intended that the scope of the invention belimited only by the proper scope to be afforded the appended claims.

What is claimed is: v

1. In a dryer section of a paper machine web drying apparatus forprofilecontrol by ventilating pockets, defined by the wrapped felt rolls, thedryer drums of one of a series of such drums, and runs of felt and thepaper web, the combination of a plurality of plenums overlying that sideof said runs of felt' from drum to felt roll which does not contact thepaper web, having a discharge chamber with its opening against the feltfor forcing air through said felt into the pockets, and sealing devicesbetween the discharge chamber and felt about the edges of the dischargechamber comprising side sealing strips of resilient material extendinglongitudinally of the felt secured to the sides of said chamberand'sloped inwardly under the chamber against the felt, a sealing stripof resilient material attached to the felt entering side of said chamberand sloped inwardly under the chamber in the direction of felt travelfor trailing engagement against the felt, a sealing strip attached toand extending across the felt-leaving end of said chamber for trailingengagement with the running surface of said felt roll, said plenum beingadapted to be placed in communicationwith a source of heated dry airunder pressure for forcing air through the felt and into said pockets.

2. The combination of claim 1 in which the sealing strip closing thefelt-leaving end of the discharge chamber is made of a stiff material,and a yieldingly acting device engages the sealing strip against thefelt roll.

3. The combination of claim 1 in which the plenum is formed with aplurality of air inlets including a central inlet and adjacent inletstoward each edge of the trailing felt, means for separately controllingthe flow of air in said inlets, and separating baffles for said inlets,each extending into close but non-contracting relation to the i feltproviding for separate plenum inlet zones and for gradual pressuretransitions between said plenum inlet zones.

4. The combination of claim 3 in which the plenum extends substantiallythe width of the felt, and is divided into three inlets including acentral inlet extending approximately one-half the total width of theplenum, and an inlet at each side thereof extending approximately thewidth of the plenum.

References Cited 7 UNITED STATES PATENTS 1,759,804 5/1930 Pieron 341602,141,403 12/1938 Offen 34155 X 2,192,432 3/1940 Bruker 34-155 2,565,5768/1951 Runton 34-155 X 3,110,575 11/1963 Justus 34--1l1 3,283,41511/1966 Schnyder u 341l1 FREDERICK L. MATTESON, 111., Primary Examiner.

A. D. HERRMANN, Assistant Examiner.

1. IN A DRYER SECTION OF A PAPER MACHINE WEB DRYING APPARATUS FORPROFILE CONTROL BY VENTILATING POCKETS, DEFINED BY THE WRAPPED FELTROLLS, THE DRYER DRUMS OF ONE OF A SERIES OF SUCH DRUMS, AND RUNS OFFELT AND THE PAPER WEB, THE COMBINATION OF A PLURALITY OF PLENUMSOVERLYING THAT SIDE OF SAID RUNS OF FELT AND THE PAPER DOES NOT CONTACTTHE PAPER WEB, HAVING A DISCHARGE CHAMBER WITH ITS OPENING AGAINST THEFELT FOR FORCING AIR THROUGH SAID FELT INTO THE POCKETS, AND SEALINGDEVICES BETWEEN THE DISCHARGE CHAMBER AND FELT ABOUT THE EDGES OF THEDISCHARGE CHAMBER COMPRISING SIDE SEALING STRIPS OF RESILIENT MATERIALEXTENDING LONGITUDINALLY OF THE FELT SECURED TO THE SIDES OF SAIDCHAMBER AND SLOPED INWARDLY UNDER THE CHAMBER AGAINST THE FELT, ASEALING STRIP OF RESILIENT MATERIAL ATTACHED TO THE FELT ENTERING SIDEOF SAID CHAMBER AND SLOPED INWARDLY UNDER THE CHAMBER IN THE DIRECTIONOF FELT TRAVEL FOR TRAILING ENGAGEMENT AGAINST THE FELT, A SEALING STRIPATTACHED TO AND EXTENDING ACROSS THE FELT-LEAVING END OF SAID CHAMBERFOR TRAILING ENGAGEMENT WITH THE RUNNING SURFACE OF SAID FELT ROLL, SAIDPLENUM BEING ADAPTED TO BE PLACED IN COMMUNICATION WITH A SOURCE OFHEATED DRY AIR UNDER PRESSURE FOR FORCING AIR THROUGH THE FELT AND INTOSAID POCKETS.